Apoptosis is cell death that occurs under various physiological conditions, which differs from necrosis occurring due to physical injuries, chemical toxicants and so forth (Kerr, J. F. and Wyllie, A. H., Br. J. Cancer, 26, pp. 239–257, 1972), and is also referred to as programmed cell death. Apoptosis is induced by cell damages by cytotoxic T cells, radiation irradiation, cytokines such as tumor necrosis factor (TNF), anti-CD3 antibodies and so forth, and apoptosis is also observed in spontaneous regression of malignant tumors. It is expected that gene therapies and destruction of specific cancer cells will become possible by using a gene or a gene product exogenously inducing cell apoptosis.
Human immunodeficiency virus type 1 (HIV-1), the causative virus of human acquired immunodeficiency syndrome (AIDS), has accessory genes (nef, vpr, vpu, and vif) which are not essential for its own replication in addition to the structural genes and regulatory genes. A gene product of vpr (protein Vpr), one of the accessory genes, has been focused as a key factor for the onset of AIDS since, for example, it increases virus infection efficiency and triggers production of viruses from latent HIV infected cells. Moreover, it has also been elucidated that the protein Vpr has a wide variety of physiological actions such as inhibition of cell growth, induction of differentiation, induction of apoptosis, inhibition of apoptosis and induction of nucleus polyploidization.